Cycles GPU Texture-duplicate memory Question
They are not the same. If I understand you correctly they are imported as different pngs and in that case they have to be loaded to gpu memory to be used. Why don't you reload one copy in node editor for all materials using this texture?

I set up a test scene with 3 cubes. Different materials for each but in the first screenshot the same texture used in the image texture node for each material. In the second screenshot there are copies of the same texture loaded and gpu memory load goes up...

Same texture in 3 different materials.


Different Textures (Copies) in each material.


Here is a screenshot of my node setup. Only one of the three different textures is in us. The other two are marked with no user by a 0 in front.